While it is anticipated that the use of virtual reality based simulators for minimally invasive surgery (MIS), with both visual and haptic (touch) feedback, would profoundly influence medical education and training leading to substantial reduction in operating room errors and morbidity as well as better patient outcomes, the current technology is quite inadequate to address the issues of realistic simulation and rendering in such simulators. The goal of the current project is to improve the realism of simulated MIS procedures by developing (1) a physically based technique for computing, in real time, the deformation of soft biological tissues as well as the reaction forces on the surgical tool as it interacts with the tissue, and (2) a scheme for enhancing visual realism which will allow the use of video images of actual surgical scenes to render "life like" images during simulation. Simulation of nonlinear behavior of tissues as well as surgical cutting are proposed. The aims are novel and involve considerable risk since (1) the physically based computational technique has been recently developed as an exciting alternative to the relatively slow performance of finite element-like techniques, but it is not known how efficient the technique is for modeling the nonlinear behavior of soft tissues or surgical cutting, and (2) the visual rendering algorithms have not been previously applied to surgical simulation. However, if successful, the schemes have the potential of becoming the standards in surgical simulation technology due to the ease with which images can be obtained for various MIS procedures and the physically based computations can be performed. Experiments involving the measurements of actual deformation fields and interaction forces will be performed to validate the simulations. While the particular focus of this project is MIS, the technology developed will be prototypes for a much wider class of medical procedures. In the long run, the existence of realistic medical simulators would accrue benefits to healthcare outside the training of residents, for instance, in the design of new surgical tools, novel surgical techniques and even alternative delivery systems for therapeutics.